1. Field of the Invention
The present invention relates to an electronic component, and more particularly, to an electronic component such as, for example, a laminated ceramic capacitor, which includes plated layers with different degrees of densification.
2. Description of the Related Art
A conventional technique involves forming an Sn plated film free of the influence of underlying metal without causing whiskers under severe conditions of a thermal cycle test (see Japanese Patent Application Laid-Open No. 2007-239076).
Sn—Pb alloy plating has been used to provide a solution, because Sn plated layers cause needle-like whiskers over time. However, from the standpoint of recent environmental protection, the demand for Pb-free solder has been increased remarkably due to tightened restrictions on the use of Pb. Therefore, the Sn—Pb alloy plating has been completely avoided, in place of solder, Sn materials have been reconsidered which are also excellent in terms of solderability, and Sn plated layers have been used for the formation of current-conducting connections such as terminals of electronic components. However, as described above, the formation of films made of such Sn plated layers makes the films likely to have needle-like Sn whiskers. If whiskers occur and grow, electrical failures due to short circuits are likely to be caused between adjacent electrodes. In addition, if the whiskers become detached and fly away from the films, the flying whiskers will cause failures due to short circuits inside and outside the system.
The technique disclosed in Japanese Patent Application Laid-Open No. 2007-239076, which is aimed at providing a member including a film which can suppress the development of such whiskers, provides a Sn plated film obtained by electrolyzation of an Sn plating solution, and the Sn plated film includes compressive stress therein, which is characteristically 1 MPa or more when measured by a spiral method.
While in general, Sn whiskers are known to be grown when compressive stress is applied to Sn films, in the Sn plating film disclosed in Japanese Patent Application Laid-Open No. 2007-239076, the Sn plated film already includes compressive stress therein, and thus, has an environment in which whiskers are likely to extend because of having no room to relax the stress. In addition, the actual evaluation of a plating bath disclosed in Japanese Patent Application Laid-Open No. 2007-239076 has failed to confirm the fact that whiskers are less likely to extend as compared with other plating baths.